The objectives of this proposal are: 1) To determine whether inhibitors of poly(adenosine diphosphate ribose) polymerase can be used to inhibit DNA repair processes. 2) To develop and evaluate combination chemotherapy protocols in which inhibitors of poly(adenosine diphosphate ribose) polymerase are used to potentiate the tumoricidal effects of DNA damaging agents. These objectives will be accomplished by systematic biochemical studies to evaluate the ability of inhibitors of poly(adenosine diphosphate ribose) polymerase to interfere with the repair of DNA strand breaks and the post-replication repair of DNA. Studies of the combination protocols will be evaluated in tissue culture and in the L1210 leukemia, MOPC 315 myeloma, B-16 melanoma, and Lewis Lung carcinoma.